Crank shaft for v-type engines and method of balancing same



April 15, c. L. WALKER 1,754,918

I CRANK SHAFT FOR V-TYPE ENGINESAND METHOD OF BALANCING SAME Filed 'July 15, 1925 2 SheetsESheet 1 I INVENTOR.

April 15, 1930- WALKER 1,754,918

CRANK SHAFT FOR V-TYPE ENGINES AND METHOD OF BALANCING SAME l atenteol Apr. 15, 1930 fiTATS CLINTON L. WALKER, F PIEDMONT, CALIFORNIA CRANK SHAFT FOR V-TYPE ENGIN B AND METHOD OF BALANCING SAME Application filed July 15,

This invention relates to a four-throw crank shaft such as is used in V-type eightcylinder engines.

In the prior types of such shafts, cranks 1 and l opposed to each other, and being at the opposite ends of the shaft, produce a strong inertia couple, which tends to rock the engine about a central transverse axis.

In and by the present invention I change the arrangement of the cranks so that cranks 1 and't are at an angle of 90 from each other, throws 2 and 3 at 90 from each other, and throw number 1 being 180 from throw number 2, and throw number 3 being 180 from thrownumber l. The advantage of this arrangement of the cranks is that it reduces the inertia couple to about one-third of what it is in prior types of crank settings where the end throws are directly opposed or at 180 from each other.

Such a shaft is not in couple balance, and the present invention includes a method of and means for putting the shaft in both static and dynamic balance with a minimum number of weights.

()ne form which my invention may assume is exemplified in the following description and illustrated in the accompanying drawings, in which Fig. 1 shows a front end elevation of the shaft;

Fig. 2 shows a rear end elevation of the same;

Fig. 3 shows a plan view of the shaft;

Fig. t shows a perspective view of the same;

Figs. 5, 6 and 7 are force diagrams, depicting the method employedin computing the size and location of the counter-balancing weights for a shaft of the type herein referred to.

In Figs. 1 to 4: inclusive I show a crank shaft having four throws or cranks, indicated at 1, 2, 3 and 4. respectively, and provided with two or more bearings indicated. at L, M and N. Throws 1 and 2 are at 180 to each other, and throws and a are at 180 to each other; but the two latter throws are at 90 from throws 1 and 2. Such a shaft may be employed in an eight-cylinder V-type 1925. Serial No. 43,703.

engine or a four-cylinder V-type engine. In the latter instance the engine would have two cylinders in each block, and the two blocks would be at 90 to each other.

As mentioned above, this arrangement of the throws greatly reduces the inertia forces tending to rock the engine end-wise, and hence the problem of dynamic balance in the shaft is considerably lessened. Of cour e the shaft is not in couple balance, and the present invention contemplates a method whereby the shaft may be placed in both static and dynamic balance.

In the diagram, Fig. 5, a, b, c, and (1 represent the longitudinal positions of the cranks 1, 2, 3, and 1, while 0 represents the central point of the shaft or the center main bearing of a three-bearing shaft. From a careful set of measurements, the product of the weight (W), times the radius of gyration (R), times the distance (L) from the central point 0 of each element of the shaft, is computed so as to determine the aggregate weight times the radius of gyration times the distance to the central point 0 of each complete crank, together with that portion of the weight represented by the connecting rods which may properly be allocated to the revolving motion of the crank pin. These products I call the VVRL of each crank.

Cranks 1 and t being the farthest from the central point- 0 have the largest products, being in the present example 104.65 as against 51.54 for cranks 2 and 3. From the diagram, which shows the VVRL of crank 1 at e, and the VVRL of crank 2 at g, it will be seen that the shaft is badly out of balance, and that the difference between VVRL of cranks 1 and 2 will have to be added parallel to crank 2 to bring the left half of the shaft into proper balanc The same considerations apply to the right half of the shaft; but as cranks 3 and 4 point to and from the reader, the diagram of Fig. 5 does not show it.

In Fig. 6, cranksl, 2, 3, and 4 are represented by lines to scale of their respective EL at e, g, c, and cl, respectively. From this it is plain that weights must be added parallel to cranks 2 and 3 equal to the differences in VVRL of cranks 1-2 and 34 respectively. Since the shaft was in static balance to start with, the addition of these Weights would throw the shaft out of static balance so that another weight at 45 and 1.414213 times each weight is added, as indicated at n. In considering static balance. the longitudinal distance from the center need not be regarded. In the present case I have elected to position the Weights at the ends of the cranks where the effect of L is the greatest. Dividing the VBL by L gives the VVR of the weights, and multiplying this by 1.414213, the VVR f the third weight to bring the shaft back to static balance is arrived at.

It will be seen from the foregoing that I attach counterbalances to each half of the shaft parallel to cranks 2 and 3, which counterbalances hax e a VVRL equal to the differences of WRL of cranks 1 and 2 and 3 and 4 respectively. To these counterbalances I add one or more weights whose centers of ravity lie on a line bisecting the angle of cranks 2 and 3. The n'iagnitude of these weights and their radius of mass center will be such that the VB shall be 1.414213 times the WR of the weight parallel to either one of the cranks 2 or 3. However, this method may be simplified so as to reduce the number of weights by composing these weights into their resultant as hereinafter pointed out.

In Fig. 7 I have indicated at A and B the WR- of two forces parallel to cranks 2 and 3, amounting in each case to 5.9843. To counterbalance these forces a third weight would have to be added at D, the resultant of A and B amounting to 8.4688. This weight would have to be added to the shaft in such a position that it would not affect the WRL balance, which would place it at the central point 0 where L is zero. This would be impossible in a three-bearing shaft, so that the weight must be divided into halves and each half moved equidistant from O on each side. In Fig. 7 I have considered each di vided weight as having been moved out to the plane of revolution of forces represented at A and B. Then on one end of the shaft there would he forces A and E acting in the same plane, and B and E similarly in their [line of revolution. Two forces working in the same plane can be composed into their resultant by completing the parallelogram of forces, and the resultant of A-E is OH, and of BE is OK. OH and OK represent by their length the amount and by their direction the position of each weight on the shaft. Hence the shaft can be put in static and couple balance by the addition of weights H and K, as shown in Figs. 1 to 4 inclusive. It will be noted that OH and OK are each equal to one-half of OC, and as OC is 1.414213 of M GA it follows that OH and OK are each equal to .7071 of OA, and that the angle of AOH is degrees.

This shaft has many advantages. It is in perfect static and running balance. It has the very important advantage over the conventional type of shaft in that it has perfect secondary balance. In this shaft the inertia couple is reduced to one-third of what it is in a shaft where cranks 1 and 4 are opposed to each other.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In a conventional V-t-ype, four-strokecycle engine, a crank shaft having four throws or cranks, cranks 1 and 2 opposed at 180 to each other and cranks 3 and 4 opposed at 180 to each other, but at 90 to the axial plane of cranks 1 and 2, and weights attached to the webs of the cranks 1 and 4 for counterbalancing the shaft both statically and dynamically, the centers of gravity of said weights being in the same axial plane but on opposite sides of the shaft and at an angle of 45 to the axia plane of crank 1, and opposed at an angle of 135 to their respective end cranks on the opposite side of the shaft to the third crank from each end respectively.

2. In a conventional V-type, four-strokecycle engine, a crank shaft having four throws or cranks, cranks 1 and 2 opposed at 180 to each other and cranks 3 and 4 at 180 to each other, but at 90 with respect to cranks 1 and 2, and coiniterbalancing weights for each half of the shaft having their centers of gravity lying in an axial plane bisecting the axial angle formed by the center lines of cranks 2 and 4 for the forward half of the shaft and cranks 1 and 3 for the opposite half of the shaft, said weights being of such mass, radius of mass center, and at such distance from the central transverse plane of the shaft as to neutralize any tendency of the shaft to gyrate about its central transverse axis.

3. A four throw crank shaft for a V-type four-stroke cycle engine, having cranks arranged in 180 degree pairs set at 90 degrees to each other and counterbalanced by a pair of weights in a plane bisecting the angles of cranks 1 and 3 and 2 and 4, and opposite thereto respectively, and each of said weights having a IVRL equal to .7071 times the difference in VVRL of cranks 1 and 2 or 3 and 4.

CLINTON L. VALKER. 

